Field of the Invention
The present invention relates to a semiconductor display device in which an organic resin film is used as an interlayer insulating film.
Description of the Related Art
In recent years, a technology for forming a TFT on a substrate has achieved a great advance, and application of the technology to an active matrix semiconductor display device which is one of semiconductor devices has been in progress. In particular, a TFT using a polycrystalline semiconductor film can operate at a high speed because it has field effect mobility higher than that of a conventional TFT using an amorphous semiconductor film. Thus, it is possible to perform control of pixels, which has been conventionally performed by a drive circuit provided outside a substrate, with a drive circuit formed on a substrate identical with a substrate on which the pixels are formed.
A TFT includes an active layer, which is obtained by adding impurities giving one conductive type to a semiconductor film, a gate electrode, and a gate insulating film provided between the active layer and the gate electrode. Further, in general, an interlayer insulating film including an insulating film is formed covering the TFT, and a wiring to be electrically connected to the TFT is formed on the interlayer insulating film.
Unless a surface of the interlayer insulating film is sufficiently planarized, when the wiring to be electrically connected to the TFT is formed on the interlayer insulating film, disconnection of the wiring is caused or the wiring becomes partially thin to increase a wiring resistance. In addition, in the case in which a pixel electrode is formed on the interlayer insulating film, unevenness is formed on a surface of the pixel electrode due to unevenness of a surface of the interlayer insulating film or a thickness of the pixel electrode cannot be uniformalized, which appears as irregularity in display.
Therefore, it is necessary to form the interlayer insulating film sufficiently thick, for example, approximately 1 to 5 μm in order to prevent unevenness from appearing on the surface of the interlayer insulating film according to a shape peculiar to the TFT.
The interlayer insulating films are roughly classified into an inorganic insulating film hereinafter referred to as inorganic resin-film and an insulating film including an organic resin having an insulating property (hereinafter referred to as organic resin film).
The inorganic insulating film is formed by chemical vapor deposition such as the CVD method or the sputtering method. Thus, in the case in which the inorganic insulating film is used as an interlayer insulating film, there is a disadvantage that treatment takes time because the inorganic insulating film has to be formed thick enough to allow a surface thereof to be planarized.
On the other hand, in the case in which the organic resin film is used, since an organic resin can be applied to a substrate on which a TFT is formed, an interlayer insulating film with a surface thereof planarized can be formed easily.
Incidentally, a wiring to be connected to a TFT is formed by forming a film having conductivity (hereinafter referred to a conductive film) on an interlayer insulating film in which a contact hole is opened and etching the conducive film.
In this case, both wet etching and dry etching can be used as the etching of the conductive film. However, the wet etching cannot cope with micronization of a wiring pattern of 3 μm or less because it is isotropic etching. On the other hand, the dry etching is capable of coping with micronization of a wiring pattern because anisotropic etching is possible with the dry etching.
However, a problem of the dry etching is that, when a conductive film on an interlayer insulating film including an organic resin film, a surface of the organic resin film is roughened. If the surface of the organic resin film is roughened, planarity of a surface of a pixel electrode to be formed on the organic resin film is spoiled, which affects display of a pixel.
In addition, organic resin is high in a water absorbing property and absorbs moisture in alkaline water solution, which is used in development, to swell. Thus, it is necessary to provide a step for subjecting the organic resin film to heating treatment after development to evaporate moisture contained therein. Moreover, even if the organic resin film is subjected to the heating treatment to evaporate the moisture, it is likely that the film absorbs moisture in an adjacent film or the atmosphere, the moisture in the film corrodes a wiring formed in contact with the organic resin film as time elapses, and long-term reliability of a panel is spoiled.